import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
public class Main {
	public static boolean result[];
	public static int dp[][];
	public static void main(String[] args) throws NumberFormatException, IOException{
		ContestScanner in = new ContestScanner();
		int n = in.nextInt();
		int count = 0;
		int max = 24*60;
		for(int i=0; i<n; i++){
			String[] s = in.nextToken().split(":");
			int start = Integer.parseInt(s[0])*60 + Integer.parseInt(s[1]);
			s = in.nextToken().split(":");
			int end = Integer.parseInt(s[0])*60 + Integer.parseInt(s[1]);
			if(start > end){
				count += (max-start) + end;
			}else{
				count += end - start;
			}
		}
		System.out.println(count);
	}
}

class MyComp implements Comparator<int[]>{
	public int compare(int[] a, int[] b) {
		return a[0] - b[0];
	}
}

class Reverse implements Comparator<Integer>{
	public int compare(Integer arg0, Integer arg1) {
		return arg1 - arg0;
	}
}

class Node{
	int id;
	List<Node> edge = new ArrayList<Node>();
	public Node(int id){
		this.id = id;
	}
	public void createEdge(Node node){
		edge.add(node);
	}
}

class ContestScanner{
	private BufferedReader reader;
	private String[] line;
	private int idx;
	public ContestScanner() throws FileNotFoundException{
		reader = new BufferedReader(new InputStreamReader(System.in));
	}

	public ContestScanner(String filename) throws FileNotFoundException{
		reader = new BufferedReader(new InputStreamReader(new FileInputStream(filename)));
	}
	
	public String nextToken() throws IOException{
		if(line == null || line.length <= idx){
			line = reader.readLine().trim().split(" ");
			idx = 0;
		}
		return line[idx++];
	}
	public long nextLong() throws IOException, NumberFormatException{
		return Long.parseLong(nextToken());
	}
	public int nextInt() throws NumberFormatException, IOException{
		return (int)nextLong();
	}
	public double nextDouble() throws NumberFormatException, IOException{
		return Double.parseDouble(nextToken());
	}
}